The Covid-19 vaccines authorized by governments around the world—including those developed by Pfizer and BioNTech, AstraZeneca, and Moderna—performed well in clinical trials, but how have they done in the real world?

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Early research suggests that, so far, the vaccines are proving very effective.

What early research reveals about the Covid-19 vaccines outside of clinical trials

For instance, in preliminary findings released Monday, one study looked at the entire 5.4 million population of Scotland between Dec. 8, 2020 and Feb. 15, when 1.14 million vaccine doses were administered. The researchers found that four weeks after a single initial dose, the risk of hospitalization declined by 85% among people who had received the Pfizer and BioNTech vaccine and by 94% among those who had received the AstraZeneca vaccine.

Similarly, preliminary data from Public Health England found that, among people ages 80 and older, just one shot of the Pfizer and BioNTech vaccine reduced cases of Covid-19 by 57% and severe cases of Covid-19 by 75%, according to Chris Whitty, England's chief medical officer. According to the Wall Street Journal, the level of protection against any "form of the disease" increased to 88% after the second dose.

In addition, the data indicated that people who do become infected after receiving the vaccine are 40% less likely to be hospitalized. Further, they were 56% less likely to die after 14 days had elapsed since their first dose of the vaccine.

Other data from the United Kingdom found that, among health care workers under 65 who had received Pfizer's vaccine, cases of Covid-19 were reduced by 72% three weeks after the first shot and by 86% after two doses, the Journal reports.

Separately, in the United States, researchers used artificial intelligence to look at the medical records of more than 31,000 people who had received either Pfizer or Moderna's vaccine at Mayo Clinic facilities in four states. According to that preliminary study—which hasn't been peer-reviewed—Covid-19 case rates were 89% lower among those who had received two doses of either Pfizer or Moderna's vaccine after 36 days had elapsed since their first shot. In addition, those who did develop Covid-19 were 60% less likely to be hospitalized if they had received either vaccine.

Those findings were echoed in two other studies focused on the Pfizer and BioNTech vaccine, which were both conducted in Israel.

One of those studies—conducted by the Israeli Health Ministry and Clalit, the largest health care provider in Israel—compared 600,000 individuals who were fully vaccinated between Jan. 17 and Feb. 6 with 600,000 unvaccinated people. Pfizer's vaccine was associated with an 89.4% drop in Covid-19 cases, including asymptomatic cases; a 93.7% drop in symptomatic cases; and a 92% reduction in the likelihood of developing a severe case of Covid-19.

The second study, conducted by Sheba Medical Center and published in The Lancet, looked at 7,214 health care workers who had received their first dose of Pfizer's vaccine in January. These individuals saw an 85% drop in symptomatic Covid-19 cases after 15 to 28 days had elapsed since their vaccinations, and they experienced an overall drop in infection rates, including asymptomatic cases, of 75%.

Experts offer cautious optimism

Experts were encouraged by these preliminary results, although they noted it's still too early to know how long protection from the vaccines will last or whether they will continue to be effective against future coronavirus variants.

Jim McMenamin, Public Health Scotland's Covid-19 incident director, said the findings of the study in Scotland are particularly important "as we move from expectation to firm evidence of benefit from vaccines."

Separately, Eran Kopel, an epidemiologist at Tel Aviv University, said the study conducted by Sheba was important, but cautioned it only focused on a single hospital and a small group of people, meaning "one could not draw clear-cut epidemiological conclusions from it."

He added, "The vaccinations are a very good tool, but this is hardly the end. This is a dynamic virus that has surprised the scientific world with its fast pace of change and variety" (Mueller, New York Times, 2/22; Kelland, Reuters, 2/22; Douglas/Colchester, Wall Street Journal, 2/22; Collis, Politico, 2/22; Langreth, Bloomberg, 2/17; Lubell, Reuters, 2/18; Weber, Yahoo! News, 2/16; Azad, CNN, 2/16).